Field of the Invention
The present invention relates to medical devices and techniques for using medical devices and, more specifically but not exclusively, to introducers for tracheal tube insertion (intubation) using direct laryngoscopes and video laryngoscopes.
Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the invention. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is prior art or what is not prior art.
Emergency intubation is accomplished through direct or video imaging of the larynx, followed by tracheal tube insertion under vision, i.e., the tube is manipulated by the operator and seen entering the larynx. Since the distal end of a tracheal tube may block direct visualization of the larynx during the insertion process, a variety of techniques have been devised to overcome this visualization challenge. In 1949, Macintosh suggested the use of a gum-elastic catheter, now commonly called a bougie, to aid in tube insertion. The bougie is a rounded tube introducer, approximately 15 Fr (i.e., 5 mm) diameter and about 70 centimeters in length, with a Coude tip that is angled slightly upward (approximately 38 degrees in the original Portex device manufactured by Smiths Medical International Ltd of Kent, United Kingdom). Throughout much of Europe and the United Kingdom, this device is considered an essential piece of equipment when inserting tubes using direct laryngoscopy.
Patient outcomes in emergency airway management show a strong correlation between adverse events and number of intubation attempts. Many operators and emergency systems advocate the use of a bougie on all initial attempts should intubation be required.
In the U.S., malleable stylets were developed for controlling the insertion of tracheal tubes. Levitan et al. has described the optimal technique for shaping a stylet as “straight-to-cuff,” to denote where the bend point of a styletted tube should be. See Levitan R M, Pisaturo J T, Kinkle W C, Butler K, Everett W W, “Stylet bend angles and tracheal tube passage using a straight-to-cuff shape,” Acad Emerg Med 2006, 13:1255-8. Levitan et al. advocate a 35-degree bend. In their opinion, this maximizes visualization, facilitates insertion, and minimizes the impaction of the tracheal tube tip on the tracheal rings.
The anterior two thirds of the trachea has cartilaginous rings that help preserve the patency of the airway. When inserting the bougie, which is flexible, and has an upturned tip, the tip will interact with the rings, creating a palpable click that is felt in 65-95% of insertions into the trachea. If the tip of the bougie is inserted into the esophagus, then these rings are not felt. The tactile feedback of being in the trachea is not perfect, however, because of several variables. If the tip rotates so that it is not directed anteriorly, then it will slide along the membranous trachea, which has no rings.
In situations of difficult laryngoscopy, the bougie may be blindly placed under the epiglottis, and, through tactile feedback, verification of tracheal insertion is provided, even when direct visualization of the glottis opening is limited. The bougie is very long (˜60-70 cm), and unfortunately it may be difficult to effectively control the distal tip, making sure that the distal tip stays upright, hugging the undersurface of the epiglottis on insertion. It is very susceptible to unrecognized rotation because of its uniformly round shape. It has no inherent directionality, apart from the distal tip, which becomes invisible after insertion. Finally, using the bougie is a two-person task. The operator places the device (while continuing to hold a laryngoscope), while an assistant helps railroad the tube. The tube cannot be preloaded on a bougie and held initially by the operator, because the tube will slide over the bougie, i.e., the two devices do not move as a unit.
Stylets have the advantage of being faster because they are inserted along with the tracheal tube. If shaped improperly, however, they can make intubation more difficult, either by blocking the line of sight, or through catching on the anterior tracheal rings. Stylet bend angles above 35 degrees, for instance, commonly cause tracheal ring impaction when using standard tubes with asymmetric left-facing bevels. See Levitan et al.
Styletted tubes do not provide tracheal-ring tactile feel, and, if the stylet is inadvertently allowed to project beyond the tube, then it can cause tracheal perforation. Even if the end of the stylet stops within the tracheal tube tip, if the stylet is too close to the tube tip, then it will stiffen the tip too much causing it to impact on the trachea. The trachea has a dimension of about 14-16 mm in female adults and about 16-20 mm in male adults. An excessive bend easily causes the tip to engage the tracheal rings. This may prevent tube insertion mechanically or result in tracheal trauma that could result in tears and other injuries. When tracheal tube advancement problems occur, the operator may need to rotate the tube (changing the bevel orientation) or stabilize the tube and remove the stylet before attempting re-insertion. In emergency situations, such delays may be consequential, and, if the intubation attempts are repeated multiple times, then there are high rates of adverse events.
Recently, hyper-angulated rigid stylets have been developed to use with hyper-angulated video laryngoscopes. Video laryngoscopes, like the Glidescope video laryngoscope from Verathon, Inc., of Bothell, Wash., use a curved tongue retractor and a video camera to image the larynx. These devices are hyper-angulated relative to the shape of a standard Macintosh curved laryngoscope blade. In order to deliver a tube to the larynx, however, a tube must follow the hyper-angulated blade around the tongue and be inserted into the trachea. Once the tip is in the trachea, the tube has to take a more-posterior angle to enter the trachea. The trachea follows the thoracic spine, i.e., it dives posteriorly. This creates a fundamental tube-delivery challenge with any hyper-angulated video laryngoscope. A stiff hyper-angulated tube—needed for rotation around the tongue—is too stiff for insertion into the trachea. It also has a side-to-side, long-axis dimension that exceeds the diameter of the trachea. See Levitan R M, Heitz J W, Sweeney M, Cooper R M, “The Complexities of Tracheal Intubation With Direct Laryngoscopy and Alternative Intubation Devices,” Ann Emerg Med 2011; 57:240-7. Numerous case reports have documented the hazards of hyper-angulated rigid stylets using video laryngoscopes.